The present invention relates to a method for producing a structure by applying nanoparticles in a suspension onto a substrate and curing with laser radiation, and to the structures thereby produced.
The term “nanoparticles” designates particles having a diameter well in the submicron range. It has been known that such particles exhibit thermophysical properties substantially different from those of the bulk materials. In particular, the melting point typically decreases substantially for particles having diameters below approximately 100 nm (nm=nanometer), and in particular below approximately 10 nm. For example, nanoparticles of gold show a melting point of approximately 300 to 400° C. at a diameter of approximately 2.5 nm while the bulk melting point of gold is 1063° C.
In WO 00/10197 this effect is exploited for producing copper structures on a semiconductor wafer at low temperatures. A suspension of copper nanoparticles in a liquid is applied to a semiconductor chip. After evaporation of the solvent, nanoparticles are concentrated in recesses in the wafer surface and the wafer is heated above the particles' melting point to sinter or melt them. This method takes advantage of the comparatively low melting point of the particles, but it requires the presence of suitable recesses in the surface of the substrate.
Published Japanese patent application JP 2000 014 101 describes a method for forming structures by focussing a laser beam into a storage tank containing a suspension of superfine particles. This method requires a large amount of the suspension and is therefore expensive.
Szezech et al in IEEE Transactions on electronics Packaging Manufacturing, Vol. 25, No. 1, pp. 26–33 have constructed fine conductor lines by drop-on-demand jet printing of nanoparticle suspended solution followed by evaporation and sintering process in an oven maintained at moderate temperature (300° C.).
However, a need exists in the art for simple and efficient devices and methods of producing structures from nanoparticles without the need for recesses on the surface in which the particles collect, or for heating of the entire substrate. The present invention relates to localized laser heating of nanoparticles to produce desired structures.